Active matrix type display

ABSTRACT

An actual concrete pixel structure of a top emission type display comprises a plurality of pixels arranged in a matrix on a substrate. Each of the pixels includes a light emission device prepared by forming a transparent pixel electrode and a metal pixel electrode on both surfaces of a light emitting layer and a driving circuits for controlling the driving current of the light emission device. The driving circuit is formed on the substrate, and the light emission device is formed in a layer manner above the driving circuit with an intermediate layer made of an insulation material interposed therebetween. The transparent pixel electrode is situated on the side opposite to the substrate. The metal pixel electrode of the light emission device is connected with the driving circuit through a conduction portion which extends through the intermediate layer. Thus, light emitted from the light emission device can be prevented from reaching transistors by locating the transistors constituting the driving circuit below the metal pixel electrode, and leak current by the light of the transistor in the off state can be suppressed to prevent degradation in the image quality.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an active matrix type display,for example, a display using light emission devices that emit light bythemselves, such as organic LEDs.

[0002] Demands for personal computers, portable information terminals,information communication equipment or composite products thereof havebeen increased with the coming of high information society. For theproducts described above, displays of reduced thickness and weight andhaving high-speed response are demanded.

[0003] As a display suitable to such demands, displays using lightemission devices capable of saving electric power have been proposed.Generally, an active matrix type display is formed by arrangingrectangular pixel regions in a matrix on a substrate. For example, anorganic LED as one of light emission devices is formed by putting anorganic LED device comprising a hole transportation layer, a chargeinjection layer and an organic light emission layer between atransparent pixel electrode (anode) and a metal pixel electrode(cathode) in such a manner that both surfaces of the organic LED deviceare in contact with the transparent pixel electrode and the metal pixelelectrode, respectively. Then, existent active matrix type organic LEDdisplays are formed by disposing a transparent pixel electrode of theorganic LED device on the side of the transparent substrate such asglass and disposing the metal pixel electrode on the side opposite tothe substrate.

[0004] In the driving circuit for the organic LED device in each pixel,a first thin layer transistor (TFT1) is disposed at a position near theintersection between each of scanning lines and signal lines arranged ina lattice, TFT1 is driven by scanning signals and pixel signals to storedate in a capacitor (holding capacitor), a second thin layer transistor(TFT2) is driven in accordance with the voltage of the capacitor and thecurrent flowing to the organic light emitting layer by way of thetransparent pixel electrode as the anode connected with TFT2 iscontrolled to emit light. Then, light emitted from the organiclight-emitting layer is taken out through the transparent pixelelectrode on the side of the substrate.

[0005] By the way, in the case of a bottom emission type display inwhich emission light is taken out from the substrate, since the area ofthe driving circuit comprising TFT1, TFT2, capacitor and lines arrangedfor each of the pixels hinders light transmission, an improvement in theso-called aperture ratio is limited.

[0006] In view of the above, to improve the aperture ratio withouteffect of the driving circuits such as TFT, the so-called top emissiontype display that takes out light from the side opposite to thesubstrate has been proposed so far (Document: SID2001 Digest-24-4L). Inthe top emission type, an improvement in the aperture ratio can beexpected as compared with the bottom emission type.

[0007] In the top emission type, light is taken out by using atransparent electrode layer on the upper side of the organic LED device,but the document described above discloses no actual structure of theorganic LED device and the driving circuit.

[0008] Further, the dielectric constant of the transparent pixelelectrode layer is generally greater by about one digit or more ascompared with that of the metal pixel electrode layer. Accordingly,current consumption increases as the size of the display panel enlarges,which poses a problem that a loss of current supply line to the organicLED device-increases.

[0009] Further, the organic LED device degrades rapidly due to heat orhumidity. Accordingly, the method of forming a transparent pixelelectrode layer in the upper portion or a method of patterning thetransparent pixel electrode layer becomes significant. In particular, torealize multi-color display organic LED devices of plural colors arenecessary. However, since light emission characteristics of devices aredifferent from one color to another color at present, it is preferred toseparate for each color lines for current supply in order to effectivelycontrol display colors. However, this involves a problem that it isdifficult to form the transparent pixel electrode layer into an optionalshape.

[0010] A first object of the present invention is to provide a specificpixel structure in the top emission type display using light emissiondevices.

[0011] A second object of the present invention is to provide a currentsupply structure to a transparent pixel electrode capable of coping withenlarging scale in the top emission type display using light emissiondevices.

[0012] A third object of the present invention is to provide a pixelstructure suitable to coloration of a panel in the top emission typedisplay using organic LED devices.

SUMMARY OF THE INVENTION

[0013] According to a first aspect of the present invention, there isprovided an active matrix type display comprising a substrate and aplurality of pixels arranged in a matrix on the substrate, wherein eachof the pixels includes a light emission device prepared by forming atransparent pixel electrode and a metal pixel electrode on both surfacesof a light emitting layer, and a driving circuit for controlling adriving current of the light emission device, the driving circuit isformed on the substrate, the light emission device is formed in a layermanner above the driving circuit with an intermediate layer made of aninsulation material interposed, the transparent pixel electrode beingsituated on the side opposite to the substrate, and the metal pixelelectrode of the light emission device is connected with the drivingcircuit through a conduction portion which extends through theintermediate layer.

[0014] With this configuration, since an aperture ratio of the lightemission device is free from the effect of the driving circuit in thelower layer, for example, a scanning signal line, a pixel signal lines,a current line allowing a driving current of the light emission devicesto flow therethrough and a transistor, the aperture ratio can beincreased. In particular, since the aperture ratio is determined only bythe conduction portion for connecting the lower layer portion and theupper layer portion, extremely high aperture ratio can be obtained.

[0015] In the case described above, the transistors for controlling adriving current of the light emission devices are preferably disposedbelow the metal pixel electrode of the light emission device. With thisconfiguration, the light emitted from the light emission device can beshielded by the metal pixel electrode and occurrence of leak current dueto the light in the off state of the transistor can be suppressed. As aresult, the potential change of the capacitor to which image data iswritten by the transistors can be suppressed to reduce the degradationin the image quality.

[0016] In particular, the metal pixel electrode covering transistors ispreferably a metal pixel electrode of the light emission device at thepreceding stage in the scanning direction. That is, when a pixel signalis written to a corresponding capacitor by the transistor, since themetal pixel electrode in the upper layer has already been selected, itis in a constant potential state. Accordingly, the effect on the writingoperation can be decreased. In addition, since current flows through themetal pixel electrode in this case, effect caused by the peripheralelectric fluctuations can also be shielded.

[0017] According to a second aspect of the present invention, there isprovided an active matrix type display comprising a substrate; and aplurality of pixel elements arranged in a matrix on the substrate,wherein each of the pixels includes a lower layer having a drivingcircuit formed thereon, an intermediate layer made of an insulatormaterial formed on the lower layer, and an upper layer having a lightemission device formed on the intermediate layer, the driving circuitincludes scanning signal lines and image signal lines disposed to crossto each other along the arrangement of the pixels, a first current linefor allowing a driving current of the light emission device to flowtherethrough, and a transistor circuit connected with the scanningsignal line and the image signal line to control the driving current ofthe light emission device by way of the first current line in responseto a scanning signal and a pixel signal, the light emission deviceincludes a light emitting layer, and a transparent pixel electrode and ametal pixel electrode that interpose the light emitting layertherebetween, the transparent pixel electrode being situated on the sideopposite to the substrate, the transistor circuit is connected with themetal pixel electrode of the light emission device through a conductorwhich extends through the intermediate layer, and disposed below a metalpixel electrode of a pixel at the preceding stage in the scanningdirection of the pixels, and a second current line is disposed in theupper layer so as to allow a driving current of the light emissiondevice to flow therethrough, and the second current line is connectedwith the transparent pixel electrode of the light emission device.

[0018] While the transparent pixel electrode of high light permeabilitygenerally has a high sheet resistance, formation of the second currentline can reduce the loss due to lines and can provide the light emissiondevices with more pixel current. In particularly, as the size of thedisplay panel enlarges, the amount of current per line increases, andthe length of the lines also increase to result in more current loss inthe current lines. Then, it is difficult to apply a sufficient voltageto light emission devices remote from a power source because of thevoltage drop along the lines; however, provision of the second currentline with low resistance enables to obtain a large sized panel.

[0019] In this case, the second current line formed in the upper layercan be extended to a portion overlapping the first current line.Further, when the capacitor for controlling the transistor that definesthe driving current of the light emission device is disposed below thefirst and second current lines at constant potential, the voltage heldin the capacitor can be held more stably to attain display of highquality. Further, the pixel signal line and the first current line arepreferably extended in one identical direction and disposedsubstantially at an equal interval. This can minimize the wiringcapacitance between the pixel signal line and the first current line toreduce the load capacitance of the transistor that writes pixel datainto the capacitor and enable high-speed operation.

[0020] Further, the second current lines are preferably disposed in alattice-like configuration along the arrangement of the pixels. This candecrease the voltage drop caused by the second current lines, which isapplicable to large sized panels.

[0021] According to a third aspect of the present invention, there isprovided an active matrix type display comprising a substrate; and aplurality of pixels arranged in a matrix on the substrate, wherein eachof the pixels includes a light emission device prepared by forming atransparent pixel electrode and a metal pixel electrode on both surfacesof a light emitting layer and a driving circuit for controlling adriving current of the light emission device, the driving circuit isformed on the substrate, the light emission device is formed in a layermanner above the driving circuit with an intermediate layer made of aninsulation material interposed therebetween, the transparent pixelelectrode being situated on the side opposite to the substrate, themetal pixel electrode of the light emission device is connected with thedriving circuit through a conduction portion which extended through theintermediate layer, and an insulative partition wall having a heighthigher than the height of the transparent pixel electrode is formed atthe boundary region between the plurality of respective pixels.

[0022] With this configuration, the light emission device can beprepared by forming a mask (for example an interlayer insulative layer)for an aperture that defines the light emission device, and vapordepositing light emitting materials of different emission colors ordissolving such light emission materials into a solvent and printingthem by means of an ink jet printer or the like, to the aperturesdefined on a color basis, thereby making it possible to cope withcoloration. That is, by arranging light emission devices emittingdifferent colors, for example, red, green and blue for each row of pixelsuccessively, and connecting the second current lines separately on acolor basis to a power source, bias voltage for light emission deviceshaving different characteristics of respective colors can be adjustedand, as a result, color images of high quality can be obtained.

[0023] According to a fourth aspect of the present invention, there isprovide an active matrix type display comprising: a substrate; and aplurality of pixels arranged in a matrix on the substrate, wherein eachof the pixels includes a lower layer having a driving circuit formedthereon, an intermediate layer made of an insulator material formed onthe lower layer, and an upper layer having a light emission deviceformed on the intermediate layer, the driving circuit includes atransistor circuit that controls a driving current of the light emissiondevice in response to a scanning signal and a pixel signal, the lightemission device includes a light emission layer, and a transparent pixelelectrode and a metal pixel electrode that interpose the light emissionlayer therebetween, the transparent pixel electrode being situated onthe side opposite to the substrate, and the transistor circuit isconnected with the metal pixel electrode of the light emission devicethrough a conductor which extends through the intermediate layer, anddisposed below the metal pixel electrode of a pixel of the precedingstage in a scanning direction of the pixels.

[0024] The light emitted obliquely from the light emission device isreflected at a transparent protective layer formed on the surface andintrudes into other pixels to possibly lower the contrast. In thisregard, when the second current line of the constitution described aboveis provided, since the light emitted obliquely from the light emissiondevice is reflected on the surface of the second current line andemitted to the outside as an emission light of that pixel, the lighttaking-out efficiency can be improved as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Other objects and advantages of the invention will becomeapparent from the following description of embodiments with reference tothe accompanying drawings in which:

[0026]FIG. 1 is a plan view showing a portion of a pixel region in adisplay according to a first embodiment of the invention;

[0027]FIG. 2 is a cross sectional view of the display taken along lineII-II in FIG. 1;

[0028]FIG. 3 is a cross sectional view of the display taken along lineIII-III in FIG. 1;

[0029]FIG. 4 is a driving circuit diagram for a pixel in a preferredembodiment according to this invention;

[0030]FIG. 5 is a plan view showing a portion of a pixel region in adisplay according to a second embodiment of this invention;

[0031]FIG. 6 is a cross sectional view of the display taken along lineVI-VI in FIG. 5;

[0032]FIG. 7 is a cross sectional view of the display taken along lineVII-VII in FIG. 5;

[0033]FIG. 8 is a plan view showing a portion of a pixel region in adisplay of a third embodiment according to this invention;

[0034]FIG. 9 is a cross sectional view of the display taken along lineIX-IX in FIG. 8;

[0035]FIG. 10 is a cross sectional view of the display taken along lineX-X in FIG. 8;

[0036]FIG. 11 is a plan view showing a portion of a pixel region in adisplay according to a fourth embodiment of the invention;

[0037]FIG. 12 is a cross sectional view of the display taken along lineXII-XII in FIG. 11;

[0038]FIG. 13 is a plan view showing a portion of a pixel region in adisplay according to a fifth embodiment of the invention;

[0039]FIG. 14 is a cross sectional view of the display taken along lineXIV-XIV in FIG. 12;

[0040]FIG. 15 is a cross sectional view of a display according to asixth embodiment of the invention, which is a cross sectional view at aposition identical with line XIV-XIV shown in FIG. 13;

[0041]FIG. 16 is a cross sectional view of a display according to aseventh embodiment of the invention, which is a cross sectional view ata position identical with line XIV-XIV shown in FIG. 13; and

[0042]FIG. 17 is an explanatory view for explaining the effect of thedisplay of the seventh embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0043] Preferred embodiments of this invention will be described withreference to the drawings.

[0044] [Embodiment 1]

[0045] FIGS. 1 to 4 show constitutional views of an active matrix typedisplay of a first embodiment. FIG. 1 is a plan view showing a portionof a pixel region in the display; FIG. 2 is a cross sectional view takenalong line II-II in FIG. 1; FIG. 3 is a sectional view taken along lineIII-III in FIG. 1; and FIG. 4 is a circuit diagram of a driving circuitfor a pixel. As shown in FIG. 4, a first thin film transistor Tsw 16 isdisposed correspondingly to each intersection between a scanning signalline 11 and a pixel signal line 12 wired in a matrix, in which a gateelectrode of the Tsw 16 is connected to the scanning signal line 11, asource electrode is connected to the pixel signal line 12 and a drainelectrode is connected to a first current line 13. Further, the firstcurrent line 13 is connected by way of a source-drain circuit of asecond thin film transistor Tdr 17 to an anode (metal pixel electrode18) of an organic LED device 25 as a light emission device. A cathode(transparent pixel electrode 19) of an organic LED device 25 is groundedto the earth. Further, a gate electrode of the Tdr 17 is connected byway of a line 10 to a capacitor (holding capacitance) Cs 15, and theother end of the capacitor 15 is connected with a drain of the Tsw 16.Then, when the scanning signal is H, the Tsw 16 turns on to hold a pixelsignal in the capacitor Cs 15, which drives the Tdr 17 as an activedevice in accordance with the voltage of the capacitor Cs 15 to controlthe current flowing to the organic LED device 25. Thus, the organic LEDdevice 18 emits light in response to the pixel signal.

[0046] The display having the driving circuits and the organic LEDdevices described above is constituted as shown in FIGS. 1 to 3. Thedisplay is divided, as shown in the cross sectional view of FIG. 2, intoa lower layer having a driving circuit formed on a substrate 26, aninsulative layer 22 as an intermediate layer formed on the lower layerand an upper layer having the organic LED device 25 formed on theinsulative layer 22. FIG. 1 shows a plan as viewed on the side of thelower layer in which a driving circuit for a portion of the pixel regionis formed; to show the relative positional relationship with the upperlayer, the metal pixel electrode 18 is shown by a dotted chain.

[0047] As shown in FIG. 1 to FIG. 3, scanning signal lines 11 (11-1,11-2) and pixel signal lines 12 are disposed as a lattice and each pixelcorresponds to a region surrounded with the signal lines. As describedlater, rectangular metal pixel electrodes 18 constituting the pixels arearranged such that each of the electrodes is displaced downward (in thedirection of row) in the drawing by about one-half pitch of arectangular region surrounded with the scanning signal lines 11 and thepixel signal lines 12. Further, the first current lines 13 are disposedsuch that each of them extends in the direction of row parallel with thepixel signal lines 12. Each first thin film transistor Tsw 16 isdisposed at a position near each intersection between the scanningsignal line 11 and the pixel signal line 12. The gate electrode and thesource electrode of Tsw 16 are connected to the scanning signal line 11and the pixel signal line 12, respectively, while the drain electrodethereof is connected by way of the line 10 to the capacitor 15 foraccumulating pixel data. Each second thin film transistor Tdr 17 forcontrolling the current flowing to the organic LED device 18 is disposedat a position near the Tsw 16 in which the source electrode is connectedto the first current line 13, the drain electrode is connected through acontact area 20 opened in the insulative layer 22 to the metal pixelelectrode 18 of the LED device 25 by way of a line 28. The upper surfaceof the insulative layer 22 is flattened on the side where the metalpixel electrode 18 is formed.

[0048] As described previously, the metal pixel electrodes 18 arepositioned while being displaced each in the direction of the row so asto cover the circuit including Tsw 16 and Tdr 17 of a pixel selectedsubsequent to the pixel of its own in the sequence of scanning. In otherwords, the circuit including the Tsw 16 and Tdr 17 is covered by themetal pixel electrode 18 selected before the pixel of its own in thesequence of scanning. For example, in FIG. 1, in the sequence ofscanning the scanning signal line 11-2 subsequent to the scanning signalline 11-1, Tsw 16-2 and Tdr 17-2 of the driving circuit for the pixelconnected to the scanning signal line 11-2 are covered at the upperportion thereof with a metal pixel electrode 18-1 connected with Tdr17-1 for the pixel driven by the scanning signal line 11-1 in thepreceding stage.

[0049] The cross sectional structure of the pixel region having thusbeen constituted will be described with reference to FIGS. 2 and 3. FIG.2 is a cross sectional view taken along line II-II in FIG. 1 and FIG. 3is a cross sectional view taken along line III-III in FIG. 1. As shownin the figures, for the thin film transistors Tsw 16 and Tdr 17, a gateelectrode 16 g is patterned on a gate insulative layer 21 formed bystacking SiO₂ on a polycrystalline silicon thin film layer 28 formed onthe upper surface of the substrate 26, and an interlayer insulativelayer 23 is further patterned, on which the pixel signal line 12 and theline 10 are connected while being in contact with the source electrodeand the drain electrode. The gate electrode 16 g can be formed, forexample, of a metal such as chromium (Cr) or aluminum (Al), or an alloymaterial thereof. The interlayer insulative layer 23 can be formed of asingle layer of SiO₂ or SiN, or a laminate thereof. Contact with thesource electrode and the drain electrode can be established by a metalsuch as Al or an alloy thereof. Further, the capacitor Cs 15 isconstituted by using, as a dielectric member, the gate insulative layer21 interposed between the polycrystalline silicon thin film 28 and anelectrode 15 a formed of the same material as the gate electrode 16 g.

[0050] As shown in FIGS. 2 and 3, in the pixel driving circuit, aportion containing the Tsw 16, Tdr 17, capacitor 15 and first currentline 13 is formed in the lower layer portion below the insulative layer22 as the intermediate layer portion. Then, in the upper layer portionabove the insulative layer 22, the metal pixel electrode 18 is patternedon the insulative layer 22. In this step, by forming an opening in theinsulative layer 22 at a position corresponding to the line 28 connectedto the drain electrode of the Tdr 17 in the layer portion connected withthe metal pixel electrode 18, a contact area 20 for connecting the metalpixel electrode 18 with the line 28 is formed at the position of theopening. Then, after covering the portion above the contact area 20 withan interlayer insulative layer 24 and forming an opening area in theupper surface of the metal pixel electrode 18, the organic LED device 25is formed by using a mask by the method such as patterning vapordeposition and, further, a transparent pixel electrode 19 is stacked onthe organic LED device 25. Then, they are sealed with a transparentsubstrate or layer such as glass or plastic with no gaps, or sealed in astate being filled with an inert gas. The transparent pixel electrode 19is formed in common over the entire display and connected with agrounding line at a periphery, not shown, of the display.

[0051] According to the first embodiment having the constitution asdescribed above, since the aperture ratio of the organic LED device 25is determined only by the contact area 20 for connecting the lower layerportion and the upper layer portion, free from the effects, for example,of the thin film transistors 16, 17, the scanning signal line 11, pixelsignal line 12 and the first current line 13 in the lower layer portion,an extremely high aperture ratio can be obtained.

[0052] Further, since the thin film transistors Tsw 16 and Tdr 17 arecovered with the metal pixel electrode 18, they are free from the effectof light emitted from the organic LED device 25 containing alight-emitting layer. As a result, since occurrence of leak currentcaused by the light in the off state of the transistors can besuppressed, the potential change of the capacitor 15 can be suppressedto reduce the degradation in image quality.

[0053] In particular, by covering the thin film transistors Tsw 16 andTdr 17 by the metal pixel electrode 18 of the pixel at the precedingstage in the scanning direction, since the metal pixel electrode 18 inthe upper layer has already been selected and at a constant potentialstate when a pixel signal is written to the thin film transistor Tsw 16by the pixel signal of the pixel signal line 12, the effect thereof onthe writing operation can be reduced. In addition, since current flowsin the metal pixel electrode 18 in this case, it has also an effect ofshielding the effect of periphery electrical fluctuations.

[0054] [Embodiment 2]

[0055] FIGS. 5 to 7 are constitutional views of an active matrix typedisplay of a second embodiment. FIG. 5 is a plan view showing a portionof a pixel region in the same manner as in FIG. 1; FIG. 6 is a crosssectional view taken along line VI-VI in FIG. 5; and FIG. 7 is a crosssectional view taken along line VII-VII in FIG. 5. This embodiment isdifferent from the first embodiment in that when the metal electrode 18is patterned on the insulative layer 22 with aluminum Al or an alloymaterial thereof, second current lines 14 are formed simultaneously. Thesecond current lines 14 are formed each at a position substantiallyequal with that of the first current line 13 in the lower layer portionin each of the pixels. The second current line 14 is connected through acontact area 27 with the transparent pixel electrode 19.

[0056] In this case, a material of high light permeability such as ITOis preferably used for the transparent pixel electrode 19. Generally,since the sheet resistance of ITO is higher by one digit or more thanthat of Al, when the transparent pixel electrode 19 itself is used forthe current line as in the first embodiment, the current supplied to theorganic LED device 25 is sometimes restricted due to voltage drop in thetransparent pixel electrode 19. In this regard, according to thisembodiment, since the second current line 14 is formed, larger pixelcurrent can be supplied to each of the organic LED devices 25 byreducing the loss due to the transparent pixel electrode 19.

[0057] In other words, as a display panel becomes larger in size, theamount of current flowing to the transparent pixel electrode 19increases while the distance along which the current flows alsoincreases; therefore, resistance is increased to increase the currentloss. Because of the voltage drop, it is difficult to apply a sufficientvoltage to organic LED devices 25 remote from a power source.Accordingly, provision of the second current lines of low resistancemakes it possible to realize a large sized display panel.

[0058] Further, since the capacitor 15 for controlling the thin filmtransistor 17 that defines the driving current for the organic LEDdevice 25 is disposed below the current lines 13, 14 at a constantpotential, voltage held in the capacitor 15 can be held more stably toprovide high quality display.

[0059] [Embodiment 3]

[0060] FIGS. 8 to 10 show constitutional views of an active matrix typedisplay of a third embodiment. FIG. 8 is a plan view showing a portionof a pixel region in the same manner as in FIG. 1; FIG. 9 is a crosssectional view taken along line IX-IX in FIG. 9; and FIG. 10 is a crosssectional view taken along line X-X in FIG. 8. This embodiment isdifferent from the second embodiment in that second current lines 14formed on the insulative layer 22 are disposed each in parallel with ashorter side of the metal pixel electrode 18. The metal pixel electrode18 is connected by way of a contact area 20 with the second thin filmtransistor Tdr 17 controlling the driving current and the second currentline 14 is connected with a transparent pixel electrode 19 by way of acontact area 27.

[0061] Since the second current lines 14 are disposed in parallel withthe shorter side of the metal pixel electrode 18, the aperture area thatcontributes to the light emission of the organic LED device 25 can bemade closer to a square shape and the aperture ratio can be increased ascompared with the second embodiment shown in FIG. 5. Accordingly, when acomparison is made on the basis of identical pixel brightness, since thecurrent density in each of the organic LED devices 25 can be reduced,the device life can be improved.

[0062] [Embodiment 4]

[0063]FIGS. 11 and 12 are constitutional views of an active matrix typedisplay of a fourth embodiment. FIG. 11 is a plan view showing a portionof a pixel region in the same manner as in FIG. 1; and FIG. 12 is across sectional view taken along line XI-XI in FIG. 11. This embodimentis different from the second or third embodiment in that the secondcurrent lines 14 are arranged as a mesh to surround the metal pixelelectrode 18. The metal pixel electrode 18 is connected by way of thecontact area 20 with the second thin film transistor Tdr 17 thatcontrols the driving current, and the second current line 14 isconnected by way of a contact area 27 with the transparent pixelelectrode 19.

[0064] In the second or third embodiment, the second current lines areformed independently on every direction of row or direction of column ofpixels. Accordingly, since the voltage drop increases in the secondcurrent line in the line in which the amount of current supply increaseseven when the width of the line is increased as compared with the linein which the amount of current supply is small, this tends to appear asthe difference of display. For example, consideration is to be made onthe case of attaining a maximum brightness 500 cd/m² at an efficiency of7 cd/A of the organic LED device 25 in a display panel having a diagonalsize of 20 inch or more.

[0065] In this case, when the current lines 13, 14 are formed by usingAl having a sheet resistance of 0.1 Ω/□ in a pixel sized 108×320 μm, thewidth of the line has to be made about 60 μm to suppress the voltagedrop to 3 V or less. Aside from the first current line 13, since thesecond current line 14 gives a direct effect on the aperture ratio, itis preferred that the line width is narrowed. In view of the above, inthis embodiment, the aperture ratio is improved by disposing the secondcurrent line 14 as a mesh, thereby decreasing the width of the lines.

[0066] [Embodiment 5]

[0067]FIGS. 13 and 14 show constitutional views of an active matrix typedisplay of a fifth embodiment. FIG. 13 is a plan view showing a portionof a pixel region in the same manner as in FIG. 1; and FIG. 14 is across sectional view taken along line XIV-XIV in FIG. 13. Thisembodiment is different from the second embodiment in that the pixelsignal line 12 formed in the lower layer portion is positionedsubstantially at the center between the adjacent first current lines13-1 and 13-2. The voltage of the pixel signal transmitted by the pixelsignal line 12 is stored in the capacitor Cs 15 by the thin filmtransistor Tsw 16 selected by the scanning signal line 11. Then, whenthe thin film transistor Tsw 16 turns off, the current controlled by thethin film transistor Tdr 17 in accordance with the voltage stored in thecapacitor Cs 15 is supplied through the contact 20 to the organic LEDdevice 25.

[0068] As described above, by disposing the pixel signal line 12 at aposition most remote from the adjacent first current line 13, theinterline capacitance of the lines can be minimized. The interlinecapacitance is in proportion with the length of the line and in inverseproportion with the distance between the lines. Since the distancebetween the first current lines 13 is determined by the pixel pitch, thesum of the interline capacitance between two adjacent current lines 13and the pixel signal line 12 is minimized when the pixel signal line 12is situated at the center of the two adjacent current lines. When thepanel size and definition of the display are increased to necessitatehigh speed driving, an increase in the load capacitance lowers thewriting speed and deteriorates the image quality. Accordingly,positioning of the pixel signal line 12 at the center of the adjacentcurrent lines 13 is optimal also so as to reduce the wiring loadcapacitance.

[0069] [Embodiment 6]

[0070]FIG. 15 is a constitutional view of an active matrix type displayof a sixth embodiment. This is a cross sectional view showing a portionat a position equal with that for the line XIV-XIV of the fifthembodiment shown in FIG. 13. This embodiment is different from the fifthembodiment in adding a process of forming a partition wall 30 made of aninsulator after forming the line 14 in the lower layer portion; thepartition wall 30 has a width equal with or less than the second line 14and is higher than the layer thickness of the transparent pixelelectrode 19.

[0071] After forming the partition wall 30, an interlayer insulativelayer 24 provided with an aperture that defines a light emitting portionis formed, an organic LED material is vapor deposited by using a maskfor organic LED devices 25 of different emitting colors while takingcare, for example, that they cover the opening defined on every colorand the organic LED material is not deposited to the contact area 27.Alternatively, the organic LED device 25 may be formed also bydissolving a light emitting material in a solvent and printed by an inkjet printer or the like. Such a stacking method of the organic LEDdevice 25 is merely an example that does not limit the invention. Afterstacking the organic LED device 25 as described above, a transparentconductive layer as a transparent pixel electrode 19 is further stackedover the entire surface. The stacked transparent conductive layer isconnected on a row of pixel basis by the partition walls 30 formed onthe second current lines 14 to separate second current lines 14,respectively, through contact areas 27.

[0072] With the manufacturing method as described above, when organicLED devices emitting light of different colors, for example, red, greenand blue on a row of pixel basis are arranged successively, bias for theorganic LED devices can be controlled in accordance with the respectivecolors by connecting the second current lines 14 separately on a colorbasis to the power source at the periphery of the display region. Sincethe light emission characteristics, such as the current and the life, ofthe organic LED devices are different from each other on a color basis,determination of the optimal bias voltage on a color basis in view ofthe color display on a display is important to displaying color imagesat high quality.

[0073] [Embodiment 7]

[0074]FIG. 16 is a constitutional view of an active matrix type displayof a seventh embodiment. This is a cross sectional view showing aportion at a position identical with that taken along line XIV-XIV ofthe fifth embodiment shown in FIG. 13. This embodiment is different fromthe second embodiment in view of the cross sectional structure of thesecond current line 14. That is, as shown in the figure, the secondcurrent lines 14 are formed covering the outer surface of protrudedridges 31 formed on the intermediate layer of an insulative layer 22.The protruded ridge 31 is formed with a width narrower than that of thesecond current line 14 and a height from ½ times to twice the thicknessof the second current line. In short, the second current line 14 isformed covering the outer surface of the protruded ridge 31 such thatthe height of the line 14 is higher than the height of the transparentpixel electrode 19 at a portion opposing to the metal pixel electrode18.

[0075] According to this constitution, it can cope with colored displayby the same effect as that of the partition wall 30 of the sixthembodiment as well as can provide an effect of increasing the amount oflight that can be taken out of the organic LED device 25 and suppressingmixing of emission light with that from other adjacent pixels.

[0076] That is, as shown in FIG. 17, in a case where the metal pixelelectrode 18 and the flat second current lines 14 are formed on the flatinsulative layer 22 having a surface unevenness of 100 nm or less, lightemitted from the organic LED device 25 transmits a surface protectivelayer 32 to the outside as an emission light. However, the lightemitting in an oblique direction as shown by an arrow 33 in the figureis reflected at the boundary of the surface protective layer 32 andpropagates in the lateral direction through the inside. As a result,this lowers not only the emission efficiency but also the contrast whenthe light is reflected at the electrode of another pixel and emittedexternally to cause degradation of the image quality.

[0077] In view of the above, to decrease the light propagating theinside as described above, the second current line 14 is constituted asshown in FIG. 16. That is, among the light beams emitted obliquely fromthe organic LED device 25, an light beam having a small incident anglerelative to the surface protective layer 32 is reflected on the surfaceof the second current line 14 having a convex cross section and is takenout to the outside as the emission light of the pixel. Accordingly, thelight taking-out efficiency can be improved as a whole.

[0078] When the display in each of the embodiments according to thisinvention described above is constituted as the top emission type, adisplay of high brightness and high image quality can be attained byrealizing pixels of high aperture ratio and suppressing the factors ofdegradation in the image quality due to light emission or electricsignals.

[0079] In the embodiments described above, while each of the thin filmtransistors 16, 17 is constituted as a top gate type, it will beapparent that an identical effect can also be obtained by constitutingeach of them as the bottom gate type.

[0080] Further, the thin film transistors 16, 17 are not restricted onlyto polycrystalline silicon but may be formed also with amorphous siliconor single crystal silicon without changing the effects of the invention.

[0081] Further, the number of the thin film transistors in the pixel isnot restricted only two but more two thin film transistors can be usedin accordance with the constitution of the driving circuit.

[0082] While the descriptions have been made of the example using ITO asthe transparent electrode 19, other conductive layer of high lightpermeability such as made of IZO may be used. Furthermore, the currentlines 13, 14 are not restricted only to Al but a metal such as copper Cuof lower resistance can be used.

[0083] As has been described above, this invention can provide aconcrete pixel structure of a top emission type display using a lightemission device.

[0084] Further, this invention can provide a current supply structure toa transparent pixel electrode capable of coping with enlarging size of atop emission type display using a light emission device.

[0085] Further, this invention can provide a pixel structure suitable tocoloration of panel in a top emission type display using organic LEDdevices.

[0086] While the invention has been described in its preferredembodiments, it is to be understood that the words which have been usedare words of description rather than limitation and that changes withinthe purview of the appended claims may be made without departing fromthe true scope and spirit of the invention in its broader aspects.

What is claimed is:
 1. An active matrix type display comprising; asubstrate; and a plurality of pixels arranged in a matrix on thesubstrate; wherein each of the pixels comprises a light emission deviceprepared by forming a transparent pixel electrode and a metal pixelelectrode on both surfaces of a light emitting layer, and a drivingcircuit for controlling a driving current of the light emission device,the driving circuit is formed on the substrate, the light emissiondevice is formed in a layer manner above the driving circuit with anintermediate layer made of an insulation material interposed, thetransparent pixel electrode being situated on the side opposite to thesubstrate, and the metal pixel electrode of the light emission device isconnected with the driving circuit through a conduction portion whichextends through the intermediate layer.
 2. An active matrix type displayas defined in claim 1, wherein the driving circuit comprises atransistor for controlling the driving current of the light emissiondevice, and the transistor is disposed below the metal pixel electrodeof the light emission device.
 3. An active matrix type display asdefined in claim 2, wherein the metal pixel electrode with thetransistor being disposed therebelow is a metal pixel electrode of thelight emission device of the preceding stage in a scanning direction. 4.An active matrix type display comprising: a substrate; and a pluralityof pixels arranged in a matrix on the substrate; wherein each of thepixels includes a lower layer having a driving circuit formed thereon,an intermediate layer made of an insulator material formed on the lowerlayer, and an upper layer having a light emission device formed on theintermediate layer, the driving circuit includes a transistor circuitthat controls a driving current of the light emission device in responseto a scanning signal and a pixel signal, the light emission deviceincludes a light emission layer, and a transparent pixel electrode and ametal pixel electrode that interpose the light emission layertherebetween, the transparent pixel electrode being situated on the sideopposite to the substrate, and the transistor circuit is connected withthe metal pixel electrode of the light emission device through aconductor which extends through the intermediate layer, and disposedbelow the metal pixel electrode of a pixel of the preceding stage in ascanning direction of the pixels.
 5. An active matrix type display asdefined in claim 4, wherein the lower layer comprises scanning signallines and image signal lines disposed to cross to each other along thearrangement of the pixels, and current lines for allowing a drivingcurrent of the light emission device to flow.
 6. An active matrix typedisplay comprising a substrate; and a plurality of pixel elementsarranged in a matrix on the substrate; wherein each of the pixelsincludes a lower layer having a driving circuit formed thereon, anintermediate layer made of an insulator material formed on the lowerlayer, and an upper layer having a light emission device formed on theintermediate layer, the driving circuit includes scanning signal linesand image signal lines disposed to cross to each other along thearrangement of the pixels, a first current line for allowing a drivingcurrent of the light emission device to flow therethrough, and atransistor circuit connected with the scanning signal line and the imagesignal line to control the driving current of the light emission deviceby way of the first current line in response to a scanning signal and apixel signal, the light emission device includes a light emitting layer,and a transparent pixel electrode and a metal pixel electrode thatinterpose the light emitting layer therebetween, the transparent pixelelectrode being situated on the side opposite to the substrate, thetransistor circuit is connected with the metal pixel electrode of thelight emission device through a conductor which extends through theintermediate layer, and disposed below a metal pixel electrode of apixel at the preceding stage in the scanning direction of the pixels,and a second current line is disposed in the upper layer so as to allowa driving current of the light emission device to flow therethrough, andthe second current line is connected with the transparent pixelelectrode of the light emission device.
 7. An active matrix type displayas defined in claim 6, wherein the first current line formed in thelower layer and the second current line formed in the upper layer areextended with being overlapped along the pixel.
 8. An active matrix typedisplay as defined in claim 7 or 8, wherein the driving circuit includesa capacitor for defining the current to flow to the light emissiondevice, and a pair of electrodes constituting the capacitor is stackedbelow the first current line with an insulative layer sandwiched.
 9. Anactive matrix type display as defined in any one of claims 6 to 8,wherein the pixel signal line and the first current line are extended inan identical direction and disposed substantially each at an equalinterval.
 10. An active matrix type display as defined in any one ofclaims 6 to 9, wherein the second current lines are disposed in alattice along the arrangement of the pixels.
 11. An active matrix typedisplay as defined in claim 6, wherein the second current line isdisposed along a shorter side of the pixel.
 12. An active matrix typedisplay comprising: a substrate; and a plurality of pixels arranged in amatrix on the substrate; wherein each of the pixels includes a lightemission device prepared by forming a transparent pixel electrode and ametal pixel electrode on both surfaces of a light emitting layer, and adriving circuit for controlling a driving current of the light emissiondevice, the driving circuit is formed on the substrate, the lightemission device is formed in a layer manner above the driving circuitwith an intermediate layer made of an insulation material interposedtherebetween, the transparent pixel electrode being situated on the sideopposite to the substrate, the metal pixel electrode of the lightemission device is connected with the driving circuit through aconduction portion which extends through the intermediate layer, and aninsulative partition wall having a height higher than the height of thetransparent pixel electrode is formed at the boundary region between theplurality of respective pixels.
 13. An active matrix type displaycomprising: a substrate; a plurality of pixel elements arranged in amatrix on the substrate; wherein each of the pixels includes a lowerlayer having a driving circuit formed therein, an intermediate layermade of an insulator material formed on the lower layer, and an upperlayer having the light emission device formed on the intermediate layer,the light emission device includes a light emitting layer, and atransparent pixel electrode and a metal pixel electrode formed with thelight emitting layer interposed therebetween, the transparent pixelelectrode being situated on the side opposite to the substrate, a secondcurrent line allowing a driving current of the light emission device toflow therethrough is formed in the upper layer such that the secondcurrent line is connected to the transparent pixel electrode of thelight emission device, and the second current line covers the outersurface of a protruded ridge formed on the intermediate layer, the widthof the protruded ridge being narrower than that of the second currentline, and the height of the second current line is formed higher thanthe height of the transparent pixel electrode at a portion opposing tothe metal pixel electrode.
 14. An active matrix type display as definedin claim 13, wherein the surface of the intermediate layer hasunevenness of 100 nm or less, and the height of the protruded ridge ismore than ½ and less than twice the thickness of the second currentline.